As is disclosed as a car-mounted power converter in Japanese Unexamined Patent Application Publication No. 2009-261136, there is known a bidirectional DC-DC converter capable of achieving high efficiency and low noise. FIG. 1 is a circuit diagram illustrating a bidirectional DC-DC converter according to a related art. In FIG. 1, the bidirectional DC-DC converter steps up a DC voltage of a DC power source V1 and supplies the stepped-up voltage to a DC power source V2. Also, it steps down a DC voltage of the DC power source V2 and supplies the stepped-down voltage to the DC power source V1. Namely, the bidirectional DC-DC converter is a circuit having a step-up chopper circuit provided with a power regenerative function so as to operate, at the time of power regeneration, as a step-down chopper circuit.
A reactor Lc includes a winding 1c having the number of turns of n3 and a winding 1a having the number of turns of n1, the windings being wound around a core (not illustrated), electromagnetically coupled with each other, and connected in series. Both ends of the DC power source V1 are connected to a first series circuit that includes the winding 1c of the reactor Lc and a switch Tr11. Connected between the collector and emitter of the switch Tr11 is a second series circuit that includes the winding 1a of the reactor Lc, a reactor La1, a switch Tr14, a switch Tr12, and the DC power source V2. The reactor La1 may be a leakage inductance between the windings 1a and 1c of the reactor Lc.
Connected between the collector and emitter of the switch Tr11 is a third series circuit that includes a switch Tr13 and the DC power source V2.
Each of the switches Tr11 to Tr14 is an insulated gate bipolar transistor (IGBT) having a gate, an emitter, and a collector.
Connected in parallel between the collector and emitter of the switch Tr11 is a diode D11, connected in parallel between the collector and emitter of the switch Tr12 is a diode D12, connected in parallel between the collector and emitter of the switch Tr13 is a diode D13, and connected in parallel between the collector and emitter of the switch Tr14 is a diode D14.
A controller 100 applies control signals to control terminals of the switches Tr11, Tr12, Tr13, and Tr14 to turn on/off these switches, thereby carrying out step-up and step-down operations of DC voltage.
The bidirectional DC-DC converter with such a configuration according to the related art turns on/off the switches to carry out the step-up and step-down operations of DC voltage. During the step-up or step-down operation, the related art realizes a soft switching operation on each switch, as well as a recovery-less turn-off operation on each diode.